The SD-10 has features beyond the extra channels. Being able to pick which switches you put your rates and mixes on is really handy. The servo slow feature (they call it delay I think) is nice when you have flaps or retracts or an engine that doesn't like having the throttle slammed open. And the better overall build quality improves the value as well. I don't fly a single plane that needs more than 7 channels, but I use the features of the SD-10 on most of them.